I really like using HWiNFO because it interfaces nicely with MSI Afterburner and I can use the OSD system to keep an eye on temperatures whilst i'm gaming...

One of things I noticed is that the Core Temp goes up as does the GPU Temp, such as when playing a DirectX 11 game vs playing a DirectX 9 game. I'm guessing the GPU fans blowing out the air out inside the case are changing the ambient temperature inside the case which is affecting the sensor checking the cores...

I am running an FX9590 AMD processor and 2x GTX 770's in SLI and whilst gaming in a DX9 game, it'll stay between 35-42C but when playing a DX11 game such as Bioshock Infinite it'll go between 42-50C and sometimes will hit 55-58C momentarily and then drop back down...